1. Field of the Invention
The present invention relates to a method for enhancing efficiency and related apparatus, and more particularly, to a method for enhancing efficiency of RRC procedure re-initiation for a user equipment (UE) in a wireless communications system and related apparatus.
2. Description of the Prior Art
The third generation mobile telecommunications system (called 3G system) provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission, and also meets all kinds of QoS requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates.
Long Term Evolution wireless communications system (LTE system), an advanced high-speed wireless communications system established upon the 3G mobile telecommunications system, supports only packet-switched transmission, and tends to implement both Medium Access Control (MAC) layer and Radio Link Control (RLC) layer in one single communication site, such as in Node B alone rather than in Node B and RNC (Radio Network Controller) respectively, so that the system structure becomes simpler.
In the LTE system, the Radio Resource Control (RRC) layer, a Layer 3 protocol, is the core of communications protocols related to Access Stratum (AS) and is located in radio network controllers (RNC) of the UNITS Terrestrial Radio Access Network (UTRAN) and a user equipment (UE). The RRC layer uses RRC messages to perform RRC procedures. RRC messages are formed from many information elements (lEs) used for embedding necessary information for setting, changing, or releasing protocol entities of Layer 2 and Layer 1, thereby establishing, adjusting, or canceling information exchange channels to perform data packet transportation.
When a UE performs a certain RRC procedure, a random access procedure is initiated accordingly, which includes a random access preamble procedure. The random access preamble procedure of the UE preferably includes transmitting a random access preamble to an evolved Node B (eNB), and receiving a random access response from the eNB.
Take a UE performing the RRC connection establishment procedure as an example. The UE transmits a random access preamble to an eNB, and after the eNB responds a random access response, the UE transmits an RRC connection request message to the eNB for establishing RRC connection. If the eNB accepts the RRC connection request, the eNB responds a RRC Connection Setup message to accomplish the RRC connection establishment procedure.
In addition, other UEs may simultaneously perform RRC procedures (such as RRC connection re-establishment procedure) initiated with a random access preamble procedure, and thereby transmits the same random access preamble on a random access channel (RACH). In this situation, the network cannot distinguish the random access preambles transmitted from different UEs, which causes contention between the UEs initiating different RRC procedures. Therefore, after receiving the random access response from eNB, each UE transmits a corresponding RRC request message (e.g. the RRC connection request message for the RRC connection establishment procedure or the RRC connection re-establishment request for the RRC connection re-establishment procedure) to the eNB. Note that, the RRC connection request or RRC connection re-establishment request message carries an initial UE identity of the UE. Although the UEs transmit the RRC request messages to the eNB respectively, the eNB only responds a corresponding RRC message, such as an RRC Connection Setup or an RRC Connection Re-establishment message, to the winner UE. In addition, the responded RRC Connection Setup or RRC Connection Re-establishment message carries the initial UE identity of the winner UE.
After the UE transmits an RRC request message (e.g. RRC connection request), and receives a response message (e.g. RRC Connection Setup) corresponding to the request message, the UE compares the initial UE identity in the transmitted RRC connection request with the initial UE identity in the received response message. If the initial UE identities are the same, namely the UE is a winner of the contention, the UE can continue performing RRC procedure. However, if the initial UE identities are different, namely the UE is a loser of the contention, the UE needs to re-initiate the random access preamble procedure immediately for restart of RRC procedure. When the UE transmits the RRC request message, a timer is started. If the UE does not receive the response message corresponding to the request message before the timer expired, the UE is considered as a loser of the contention and the random access preamble procedure is re-initiated. Since the response message can be used for determining the result of contention of UEs, the response message is called a contention resolution message.
In the prior art, if the UE receives the response message which is not expected (such as if the UE transmits the RRC connection request, but receives the RRC Connection Re-establishment, or if the UE transmits the RRC connection re-establishment request, but receives the RRC Connection Setup), the UE does not respond. Since the UE receives the unexpected response message and thereby does not respond, the UE does not re-initiate the random access preamble procedure to restart the RRC procedure until the timer expires, which causes a time delay of RRC procedure re-initiation and affects quality of the wireless communication service.